Do long-distance migratory birds track their niche through seasons?

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Aim: Seasonal migration by animals is an extensively studied, global phenomenon.Yet, we still lack a general understanding whether migrants track their niche between summer and winter ranges (following fixed environmental conditions throughout the year) and which mechanisms influence this behaviour. Here, we assessed the degree of seasonal niche tracking in Holarctic long-distance migratory birds (n = 717; excluding very rare species) and evaluate the influence of biogeographic (regional and range characteristics) and ecological (trophic) factors on tracking. Location: Global. Taxon: Birds. Methods: We calculated seasonal niche overlap by means of ordination, and estimated the degree of niche tracking using similarity tests. Niche tracking was evaluated for two different environmental predictor sets: climate and vegetation productivity (reflecting resource selection) versus climate and land cover (reflecting habitat choice). Multivariate phylogenetic regression was used to evaluate effects of biogeographic and ecological traits on niche tracking. Results: We found significant niche tracking in 65–95% of species with a higher proportion of species significantly tracking climate and land cover compared to climate and vegetation productivity. Traits explained 12–18% of the variance in niche
tracking with strong regional differences, a negative effect of migration distance and positive effects of range size on niche tracking. The effects of niche breadth and trophic traits were less pronounced and varied between environmental predictor sets. Main conclusions: Our results indicate that at coarse spatial resolution, long-distance migratory species tend to track their niche and select largely similar environments through seasons. Stronger niche tracking of land cover could reflect conservatism in habitat selection across seasons, for example for foraging and roosting. This conservatism towards land cover should be considered when making predictions to future environments. A better understanding of the factors that constrain seasonal range limits will be critical for predicting how migration patterns could respond to future environmental changes.